Synchronous Intravital Imaging and Cavitation Monitoring of Antivascular Focused Ultrasound in Tumor Microvasculature Using Monodisperse Low Boiling Point Nanodroplets

Abstract

Focused ultrasound-stimulated microbubbles can induce blood flow shutdown and ischemic necrosis at higher pressures in an approach termed antivascular ultrasound. Combined with conventional therapies of chemotherapy, immunotherapy, and radiation therapy, this approach has demonstrated tumor growth inhibition and profound synergistic antitumor effects. However, the lower cavitation threshold of microbubbles can potentially yield off-target damage that the polydispersity of clinical agent may further exacerbate. Here we investigate the use of a monodisperse nanodroplet formulation for achieving antivascular effects in tumors. We first develop stable low boiling point monodisperse lipid nanodroplets and examine them as an alternative agent to mediate antivascular ultrasound. With synchronous intravital imaging and ultrasound monitoring of focused ultrasoundstimulated nanodroplets in tumor microvasculature, we show that nanodroplets can trigger blood flow shutdown and do so with a sharper pressure threshold and with fewer additional events than conventionally used microbubbles. We further leverage the smaller size and prolonged pharmacokinetic profile of nanodroplets to allow for potential passive accumulation in tumor tissue prior to antivascular ultrasound, which may be a means by which to promote selective tumor targeting. We find that vascular shutdown is accompanied by inertial cavitation and complex-order sub-and ultraharmonic acoustic signatures, presenting an opportunity for effective feedback control of antivascular ultrasound.

Photoactivated Gas-Generating Nanocontrast Agents for Long-Term Ultrasonic Imaging-Guided Combined Therapy of Tumors

“…Using long-term ultrasonic imaging, the in vitro therapeutic ability of PGNAs to kill cancer cells was evaluated based on the production of reactive oxygen species (ROS). − Flow cytometry was then performed to verify the ROS generation ability of PGNAs under irradiation with focused ultrasound, used mostly in sonodynamic therapy and drug delivery. ,− To test whether the anticancer ability of PGNAs was related to the production of ROS, we first used a commercial probe, 2,7-dichlorodihydrofluorescein diacetate (DCFH-DA), and then detected the intracellular ROS levels of PGNAs-treated cancer cells by the flow cytometry. As expected, the PGNAs induced significant ROS generation (Figure S31).…”